See pic. That is my current setup that gets air when i bleed it. Less then 1 second of tiny bubbles shortly after i open bleed port. Heater never cycled off for 45 minutes as i bleed it over and over. If the bleed was closed < 20 seconds, then no bubbles, but if it was open >30 seconds, there was tiny bubbles,but for less then 1 second. Several times I had it open for 30 to 45 seconds after bubbles stopped and never saw any more. Until i closed it for 30 or more seconds.

Ideas? e

  • Ignore syphon in fuel bucket. Copper tubing goes into fuel and syphon is not used.
    – Paul Mars
    Commented Feb 19 at 21:17

2 Answers 2


The pump on the oil burner sucks oil from the tank.

If it's picking up air, there's a tiny leak (possibly so tiny oil isn't visibly leaking out, or possibly just in a place you haven't noticed it, yet) where air is getting sucked in.

Guy working on a furnace (that kept crapping out) at a workplace mentioned that it's particularly problematic with lines that run overhead to the furnace (as that one did) rather than along the floor as any bubbles collect. It appears that that might be the case here as well.

  • My entire line is 46"
    – Paul Mars
    Commented Feb 20 at 18:15
  • Ok this site carriage return means add comment. Then Too long by 111 characters
    – Paul Mars
    Commented Feb 20 at 18:18
  • Part one: Ok on this site line space means add comment. For this test I replaced the pump flare fitting with new. Im always reluctant in tightening for fear of over tightening. It is quite tight, but i could get another 1\4 or even 1\2 turn, but if i turn it any more, ill need to do one full complete turn and i fear that would be over tightening and may be even be possible. To be continued
    – Paul Mars
    Commented Feb 20 at 18:19
  • Part two: I did cover threads with dope and let it sit after tightening for 48 hours before turning heater on. If it is pulling in air it only does for under 1 second. Maybe by opening bleed port im reducing the pressure differential and that stops air from being pulled in. Another words it might be pulling in air continually when bleed port is closed.
    – Paul Mars
    Commented Feb 20 at 18:20
  • you spent 48 hours tightening the fitting?
    – ron
    Commented Feb 20 at 20:44

Several times I had it open for 30 to 45 seconds after bubbles stopped and never saw any more. Until i closed it for 30 or more seconds.


my first is for you to work on your written english...

if I correctly interpret what you have written, and I correctly assume what is happening even though it is not evident in your pic... the pump is not holding its prime. given the current setup pulling a 4' line from a pail having enough fuel in it to not suck air from the pail, once the burner stops after some amount of time the fuel will drain from the copper tube back into the pail given the orientation, then with it being a one-pipe setup air in that supply tube from the pail becomes a problem on burner start until you bleed it then it'll run fine and never cycle off for 45 minutes. Until the burner does cycle off, and then the pump doesn't hold its prime and oil drains out of the line and air gets in and the problem recurs on subsequent start.

Another idea is, based on what you described (and didn't) what actually is the problem? Do you normally operate your burner from an open 5-gal pail right next to it and you're playing and don't understand what's happening, or does the burner actually have a restart problem when all the plumbing is coming properly from the oil tank wherever that is?

Part two: I did cover threads with dope and let it sit

  • you don't need to let dope sit, if you do you're doing something wrong
  • the seal is not on the threads, it's at the flare fitting; you having said this also makes me think you have a bad connection (as in not recognizing how a flare connection works) but if that was the case there would be evidence as you will have a recognizable oil seepage leak there... put a white paper towel around/under any flair fitting between burner and tank and see if there is red wetness after a day.

last idea - call an oil company for tech service, replace the pump, check the lines and level at which they run from the tank to burner, get a basic burner tuneup, if u actually have a problem with the unit not running reliably.

  • final idea - your part one: to get over your fear/ignorance of flare connections buy a flaring tool, get some tubing, practice, hook up to your air compressor and pressurize to test using soapy water on outside of joint, or geek out and use a vacuum pump and gauge and see how well it holds vacuum.
    – ron
    Commented Feb 20 at 21:17
  • After tightening fittings. Running for 30 seconds with no bubbles, then his for a few seconds. Then bubbles stopped (2nd pic), then bubbles again.
    – Paul Mars
    Commented Feb 21 at 20:16
  • ibb.co/0Y2m3jt ibb.co/MC5j4Z7
    – Paul Mars
    Commented Feb 21 at 20:19
  • Furnace did NOT cycle off for 45 minutes. Dope label says wait 48 hours.
    – Paul Mars
    Commented Feb 21 at 20:24
  • Ive never had an issue with my flairs, but i also never get too confident
    – Paul Mars
    Commented Feb 21 at 20:25

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